(1) Field of the Invention
This invention relates to blowing agents of tetrazoles and their derivatives which are used as foaming agents for precision molding of resins or reducing the weight of resin molded products, inflators for automobile air bags, or smoking agents for effectively diffusing agricultural chemicals such as insecticides and bactericides, or chemicals such as anti-contamination agents and aromatizing agents.
(2) Description of the Prior Art
Since crystalline resins, of course, crystallize and shrink during cooling steps after molding, it has been difficult to obtain a molded body having the same precise dimensions as its mold base. This apparent shrinkage in precision molding has been avoided by experimentally adjusting the size of the mold base. However, it has been difficult to obtain molded bodies with complete precision by the conventional processes. To prevent the molded bodies from shrinking, pneumatic pressure was applied into the core portion of the molded bodies (Japanese Patent Publications SHO 48-41264, SHO 57-14968) or an addition of more expensive foaming agents was proposed (Japanese Patent Laid-Open Publications SHO 50-129563, SHO 53-12864, SHO 56-61435, and U.S. Pat. No. 4,871,861). In the latter case, however, there have been available no satisfactory foaming agents for thermoplastic resins having high melting points, and therefore there have been no quality high foaming molded products.
Also, conventionally, sodium azide has been used as the inflator for air bags for automobile safety protection. Since sodium azide has a problem of toxicity, blowing agents of tetrazoles and their derivatives have been proposed as a countermeasure for the toxicity (Japanese Patent Laid-Open Publication SHO 46-906, DE 2,150,465, Japanese Patent Laid-Open Publications SHO 49-87583, SHO 50-75592, SHO 57-123885, SHO 57-123886, HEI 2-225159, HEI 2-184590, U.S. Pat. No. 4,948,439, Japanese Patent Laid-Open Publications HEI 2-221179, HEI 2-225389, and U.S. Pat. No. 5,035,757).